A Dinoflagellate Cyst From Antarctic Sea Ice1

The small (< 15 μm) hypnozygote of an autotrophic athecate dinofiagellate found in association with Antarctic sea ice had an external covering composed of approximately 60 plates, each of which was bounded by sutural ridging and possessed an intratabular process. A cingulum and sulcus were also evident. The ultrastructure of the cyst was increasingly dominated by storage bodies as the cyst matured, and the cell wall thickened from 0.2 to 0.8 μm over 2 months. This cyst has been encountered often but usually at low abundances (103−104 cells·L−1); however, the maximum abundances observed (106 cells·L−1) indicate that the formation of this cyst may play an important part in the ecology of sea ice communities.